The present invention relates to a clocking circuit for providing periodic clocking or timing signals in an electronic circuit. The invention includes a primary clock source and a back-up clock source, the latter of which is enabled to provide clocking signals upon detection of a fault in the primary clock source.
Modern electronic circuits, particularly those used in connection with microprocessor-based systems, typically require accurate clocking, or timing, signals that are used to synchronize the various electronic functions of the circuit. Generally, a single master clock source, such as a clock oscillator, is employed to provide a periodic clocking signal at a single frequency. This clocking signal can be divided by various numerical values to result in a plurality of separate clock signals, all of which are at a fraction of the master clock signal for uses at various portions of the circuit.
Accurate clock signals are essential for a proper functioning of the electronic circuit. If the frequency of the master clock signal deviates from its predetermined clock frequency, the circuit will not perform in the manner as intended.
Thus, a need exists for a system that monitors and checks the master clock oscillator to determine if the frequency of the clocking signals deviates from its predetermined clock frequency and to compensate for such deviation if it exists. This need is particularly important in those working environments that impose a greater risk of oscillator faults. For example, electronic circuits that are implantable in the human body, such as pacers, cardioverters, or defibrillators impose a risk of seepage of body fluids into the circuitry housing which could adversely affect the integrity of the clock oscillator. In such environments, accurate monitoring of the clocking signals becomes particularly important.